Butadiene-methylal addition products



Patented Oct. 10, 1950 UNITED STATES PATENT OFFICE BUTADIENE-METHYLAL ADDITION PRODUCTS No Drawing. Application October 5, 1949, Serial No. 119,761

Claims. 7 1

This invention relates to novel organic compounds and more particularly to certain reaction products of butadiene and methylal. We have discovered that a, number of novel organic compounds may be prepared by reacting methylal and butadiene'inthe presence of sulfuric acid, among which we have identified 3,5- dimethoxy-l-pentene; 1,5-dimethoxy-2-pentene; 3-methoxy-4methoxymethylperhydropyran; and 1,2,5-trimethoxy-3-methoxymethylpentane. The first two of these novel compounds result from the addition of one mol of methylal to one mol of butadiene; the third from the addition of one mol of methylal and one -mol of formaldehyde to one mol of butadiene; and the fourth from the addition of two mols of methylal to one of butadiene.

In preparing our novel compounds, methylal and concentrated sulfuric acid are mixed, and butadiene is bubbled into the mixture under atmospheric pressure until the desired quantity has been absorbed. The sulfuric acid acts both as a catalyst and as a solvent in the reaction and we have found that it is necessary to use at least one part of sulfuric acid to twelve parts by weight of methylal, since with lesser amounts of sulfuric acid the reaction mixture tends to split into two phases upon addition of butadiene, and the total absorption of butadiene is small. For ease in handling, and to insure rapid absorption of butadiene, we prefer to use about one part by weight of sulfuric acid to about three to four parts of methylal, although greater quantities may be used without deleterious effects upon the reaction. Use of larger quantities of acid is not economically desirable, however, since the excess acid must be neutralized prior to separation of the reaction products from the mixture, and is therefore lost.

The reaction may be carried out at any convenient temperature. Generally speaking, however, we have found that the butadiene is absorbed more readily by the solution as the temperature is lowered, and the time required to react the desired quantity of butadiene is greatly shortened. Thus in one run at 25-30 C. it was found that 75 grams of butadiene was absorbed by a solution of 600 ml. of methylal in 150 ml. of sulfuric acid in three and one-half hours; whereas in another run at 0-10 0., using the same quantities of methylal and sulfuric, 230 grams of butadiene were absorbed in two and one-half hours. Obviously, in commercial applications of our process, the cost of refrigeration would have to be balanced against the increased yields obtainable by cooling .in order to determine optimum commercial conditions. For laboratory work, however, We prefer to operate at about 0-10 C.

The quantity of butadiene added to the reaction mixture has an important effect on the product distribution, although all products of reaction are present in the mixture after reaction to some extent. It has been observed that the lower-molecular-weight products, such as the dimethoxypentenes, are produced almost exclusively by increasing the amount of butadiene to approach equimolarity with the methylal. A very large excess of methylal causes a shift to the production of higher molecular weight products, although some of the lower ones are still produced.

After the reaction is complete, the mixture is neutralized by addition to caustic in amount equivalent to the original amount of sulfuric acid present. The neutralized material is then refluxed for a time sufiicient to assure complete hydrolysis of any sulfuric esters or intermediate compounds, and is then steam-distilled to remove unreacted methylal and the lower-boiling products of reaction. It has been found desirable to remove the lower-boiling compounds by steam distillation, since ordinary distillation under atmospheric pressure will raise the temperature within the still pot to point at which decomposition of the heavier reaction products will take place.

The steam distillate is then saturated with so dium sulfate and extracted with ether or other suitable solvent to remove the reaction products. After evaporation of the solvent, the extract may be fractionated to recover 3,5-dimethoxy-l-pentene, boiling at 136.5-l3'7 C. at 745 mm., and 1,5-dimethoxy-2-pentene, boiling at MBA-164 C. at 745 mm.

The residue from the steam distillation is also solvent-extracted to remove higher-boiling products of the reaction. After evaporation of the solvent, the extract may be fractionated under vacuum to recover 3-methoxy-4-methoxymethylperhydropyran, boiling at 98 C. at 10 mm., or 107 C. at 30 mm.; and 1,2,5-trimethoXy-3-methoxymethylpentane, boiling at 137 C. at 35 mm. or 14l.5 C. at 40 mm.

An example of a method of preparation of our new butadiene-methylal reaction products is as follows: 200 ml. of sulfuric acid was added slowly with mechanical stirring to 700 ml. of methylal which had previously been cooled in an ice bath. The mixture was kept in the ice bath until the sulfuric acid had been completely added. While the stirred mixture was held at -10 C. butadiene gas was bubbled through the mixture with a gas diffuser having good capillary porosity and a large surface. At the end of one and one-half hours it was found that 121 grams of butadiene had been absorbed. The stirring was then continued for an hour, after stopping addition of butadiene, to drive out any excess of butadiene which might have been dissolved in the reaction mixture, and the mixture was allowed to stand overnight at room temperature to achieve equilibrium.

The mixture was then neutralized by adding it to a cool solution of sodium hydroxide exactly equivalent to the original amount of sulfuric acid present, and the neutralized batch was then refluxed for about one hour to assure complete hydrolysis of any esters or other intermediate compounds. The refluxed batch was then steam-distilled and the steam distillate was taken off in the following fractions: A 50 C. fraction (260 ml.) essentially methylal; a '-70 C. fraction ml.) consisting mostly of methanol produced in the reaction but giving. tests also for carbonyl groups and unsaturation; a -95 C. fraction (50 ml.) of highly unsaturated material with a seeming plateau at 92 C., which we have not identified; and finally a 95-100 C. fraction. The steam distillation was continued until a test sample of the distillate yielded no separate layer when saturated with sodium sulfate.

The 95-100 0. fraction of the steam distillate was then saturated with sodium sulfate and extracted seven times with ether, yielding about 150 ml. of product when the ether was stripped off. This steam-volatile extract was then roughly distilled through an eight-ball Snyder column to effect further separation of the high boiling material from the lower-boiling fractions. This preliminary fractionation indicated plateaus around 140 and 166 C., a single fraction of boiling-point range l30-l75 C. being collected, consisting of about ml. Some 20 ml. of higher-boiling product remained in the still pot, this residue being later added to the higherboiling materials recovered from the bottom of the steam distillation. The -l75 C. fraction was then precisely rectified to secure pure cuts for the determination of physical constants and structural analysis, normal-butyl phthalate being used as a booster liquid in the still pot to minimize overheating because of low volume. Two cuts were isolated in this distillation, one cut boiling at 136.5-137 C. at 745 mm., the other out boiling sharply at l63.4 C. at 745 mm. These cuts will be designated as Cuts V and X, respectively, for convenience.

The non-steam-volatile material was then extracted from the neutralized bottoms of the steam distillation with ether, the solution being extracted eight times to recover as much of the higher-boiling materials as possible. This extract was then stripped of ether and vacuumdistilled rapidly to separate the materials from any decomposable material that may have been present. A fraction (125 ml.) boiling up to 250 C. at 40 mm. pressure was collected. At this temperature decomposition began to set in and it was deemed inadvisable to collect any further fractions. About 45 ml. of very highboiling material was left in the distillation flask after rectification.

The 20 ml. bottoms from the rectification of the steam-volatile extracts were added to the roughly distilled non-steam-volatile extract, and the mixture was fractionated in an Oldershaw column for the purification of higher cuts, normal-butyl phthalate being used as a booster to increase the recovery of desired cuts and to minimize decomposition by keeping the still pot full enough to prevent local overheating. A fraction designated as Cut Y was obtained boiling at 98 at 10 mm. The total yield of this fraction was 40 ml. Further distillation yielded a fourth cut designated as Cut Z which boiled at 137 at 35 mm., this being obtained in yield of 12.2 ml. As has been pointed out before, still higher-boiling cuts in the non-steam volatile fraction were noted in the first rough distillation ofthe fraction. Yields of the various designated cuts, based on butadiene, were as follows: Cut V, 12 per cent; Cut X, 20 per cent; Cut Y, 13 per cent; and Cut Z, 3 per cent.

Cut Z had an experimental molecular weight, by freezing point depression of benzene, of and. 204, on two determinations. This corresponds closely to the theoretical molecular weight of 206 for a compound having an empirical formula C10H22O4, which would result from the addition of two mols of methylal to one of butadiene. Further confirmation of this empirical formula and the structure assigned is found in the experimental properties of Cut Z as compared with the theoretical for C10H22O4, as set forth in the following table.

Qualitative tests indicated methoxyl: positive; hydroxyl: negative; unsaturation: negative; carbonyl: trace positive; ester; negative; acidity: negative; and ether: positive.

Due to the fact that in a Prins acid-catalyzed addition, such as the present reaction, the negative-acting group is always observed to go to the olefinic carbon which has been more heavily substituted with electronegative groups, it is believed that the reaction mechanism involves an initial 1,4 addition of methylal to butadiene and then a 2,3 addition of the second molecule of methylal to the remaining double bond to give 1,2,5-trimethoxy-3-methoxymetliylpentane, and. that our Cut Z is this previously unknown compound.

It ispossible that the other orientation, that is, initial 1,2 addition with subsequent 3,4 addition, could also take place to give 1,3,4,6-tetramethoxyhexane, which, however, due to its greater chain length, would be expected to have a higher boiling point than the structure assigned to Cut Z. If the second isomer is produced in the reaction, it would probably be found in the higher-boiling material left behind in the still pot when the non-steam-volatile extract was distilled under vacuum.

While Cuts V, X, and Y above have been identified as dimethoxypentenes and 3-methoxy-4- methoxymethylperhydropyran, respectively, these compounds are not claimed in this application,

The four compounds which we have isolatedare of a comparatively newtype and oifer many possibilities as plasticizers and chemical intermediates. Thus a cleavage of the methoxyl groups would yield new polyhydroxy alcohols of the types being currently used as insect repellents and insecticides. It has also been observed that our new compounds are apparently good solvents for the silicone type greases as evidenced by troubles encountered with maintaining sufficient stop-cock lubrication, especially during vacuum distillation.

Having now described the invention, what is claimed as new and useful is:

1. 1,2,5-trimethoxy-3-methoxymethylpentane.

2. The method of preparing 1,2,5-trimethoxy- 3 methoxymethy1pentane including dissolving methylal in concentrated sulfuric acid, reacting butadiene with the dissolved methylal, neutralizing the reaction mixture, steamdistilling the reaction mixture to remove unreacted methylal and the lighter reaction products, and recovering 1,2,5-trimethoxy-3-methoxymethylpentane from the non-steam-volatile portion of the reaction products.

3. The method according to claim 2 in which sulfuric acid is present in the methylal-sulfuric acid solution in the amount of at least one part by weight of sulfuric acid to twelve parts of methylal.

4, The method according to claim 3 including extracting the non-steam-volatile portion of the reaction products with a solvent, stripping the solventfrom the extract, and recovering 1,2,5- trimethoxy-3-methoxymethylpentane by fractional distillation under vacuum.

5. The method according to claim 4 in which the solvent is ether.

OTIS C. DERMER. JOHN J. HAWKINS.

No references cited. 

1. 1,2,5-TRIMETHOXY-3-METHOXYMETHYLPENTANE. 